It is known for a washer to have slots extending radially outwardly from its inner edge so as to allow it to be pushed with a ratchet action along a stud. The washer may merely form part of a larger fastening device such as a cap or a nut as described hereinafter. The stud may be formed with just a single circumferentially-extending rib or groove with which the washer is to ratchet into engagement. More usually, however, the stud would be formed with a longitudinally-extending series of the ribs or grooves. Again, the stud may merely form part of a larger workpiece.
If the washer is not intended to be removable from the stud, it may form part of a cap so as to conceal or protect the free end of a ribbed or grooved stud, and may be much more difficult to pull-off than to push-on.
If the washer is intended to be removable from the stud, it may form part of an internally threaded nut having external torque faces for allowing the nut to be rotated relative to an externally threaded stud, such a nut sometimes being referred to as a knock-on/screw-off nut.
A particular disadvantage of this known prior art arises when the stud is resiliently mounted so that the stud travels for an undesirable distance with the washer, cap or nut, with no relative movement therebetween, as an attempt is made to drive the washer, cap or nut longitudinally onto the stud thereby requiring relative movement therebetween.
It is known, for example, for an externally threaded stud to be carried by means of a layer of foamed material forming part of a seat for a vehicle. The free end of the stud is to pass through an aperture in a seat panel, or an aligned pair of apertures in a twin-skin seal panel, so as to permit fastening with an internally threaded nut. It would be desirable for the nut to be a knock-on/screw-off nut. However, the foamed material is such that it would resiliently compress if an attempt was made to drive or knock the nut onto the stud. The free end of the stud might be pushed back through or into the seat panel before the nut could ratchet into engagement with the stud. Even if the nut could be secured to the stud, the foamed material carrying the stud would resiliently return to its original condition when the driving force on the nut was removed. This would move the nut away from the seat panel thus resulting in an unacceptably loose fixing of the foamed material to the seat panel.